SaaS billing encompasses the full lifecycle of financial transactions in a subscription software business, from generating invoices and collecting payments to handling upgrades, downgrades, proration, and revenue recognition. It differs from traditional billing due to its recurring, usage-based, and multi-currency complexity.

Example: A SaaS company uses a dedicated billing platform to manage 5,000 active subscriptions across monthly and annual plans, automatically handling renewals, proration on upgrades, dunning for failed payments, and compliant revenue recognition.